Streaming radio and music recommendation service Last.fm now streams full length tracks and even albums on-demand, making it the largest completely legal source of free, on-demand streaming music on the web. Any single track can be played up to three times before you're prompted to join their yet-to-be-released subscription service, which will offer unlimited plays of any song. Currently the service is available to the US, UK, and Germany, but Last.fm is working to expand to other countries. If the new service has piqued you interest in Last.fm, check out these 15 Last.fm power tweaks for more ways to take advantage of the excellent music service.